The Oxo process is well known in the art and is generally described in detail in Kirk-Othmer, Encyclopedia of Chemical Technology, Volume 16, 3rd ed., John Wiley & Sons, pp. 637-653, 1981.
In the well known Oxo process, olefins are hydroformylated by reaction with carbon monoxide and hydrogen, generally charged as synthesis gas (syn gas) mixtures, in the presence of a cobalt Oxo catalyst in dissolved form to form a mixture of Oxo aldehydes and alcohols. This Oxo reaction is typically carried out at syn gas pressures of from about 10.33 MPa to 31.00 MPa (1500 to 4500 psig) and at temperatures of from about 65.degree. C. to 230.degree. C. Thereafter, the product mixture containing the alcohols and aldehydes is recovered and can then be treated by known means to hydrogenate the aldehydes to form additional quantities of the corresponding alcohols. These alcohols, in turn, are widely used as chemical intermediates in the manufacture of plasticizers, detergents, solvents, and the like.
Prior to the hydrogenation step, the crude Oxo reaction effluent, which contains dissolved cobalt catalysts, the aldehyde and alcohol products and reaction by-products together with any metallic contaminants, is generally treated to remove the dissolved cobalt catalyst, which then for reasons of economy must be recycled to the Oxo reactor.
"Demetalled" hydroformylation reaction product or crude Oxo alcohol product is the reaction product which is substantially depleted of the transition metal cobalt catalyst required for the hydroformylation reaction. Such crude Oxo product will generally contain cobalt in an amount of from about 0.05 to 3.0 wt. %, calculated as elemental cobalt. The concentration of aldehyde in the crude Oxo alcohol product is generally from about 20 to 75 wt. %.
The next step in the Oxo process is the hydrogenation of the crude alcohol product which is typically carried out at pressures of about 4.83 MPa to 31.00 MPa (700 to 4500 psig) using sulfided bimetallic cobalt and molybdenum oxides or nickel and molybdenum oxide supported on alumina as the hydrogenation catalyst. Because of the high content of carbonyl-containing compounds present in the crude alcohol product the use of relatively high pressures with the traditional bimetallic catalysts has been required in order to achieve the desired yield of alcohol product.
The use of bimetallic catalysts in the hydrogenation of crude alcohol Oxo product is disclosed, for example, U.S. Pat. No. 5,030,774, issued Jul. 9, 1991, and European Application 89304856.1, published Nov. 29, 1989. The present invention is based on the discovery that certain multimetallic catalysts are useful in the two separate hydrogenation steps practiced in the cobalt catalyzed Oxo process.
A parallel Rhodium catalyzed Oxo process is known in the art. The rhodium oxo process employes various catalyst forms including ligand-modified rhodium, rhodium modified with ionic phosphine ligands, and unmodified rhodium catalyst. The ligand-modified rhodium hydroformylation process is typically carried out at low pressures [0.7-3 MPa (100-450 psi)] and low temperatures (80.degree. C.-120.degree. C.). The ionic phosphine ligand process is typically carried out at higher temperatures greater than 125.degree. C. and pressures in excess of 6 MPa. The Rhodium oxo process is discussed in Kirk-Othmer, Encyclopedia of Chemical Technology, Volume 17, 4th ed., John Wiley & Sons, pp. 902-919, 1996, the entirety of which is hereby incorporated by reference.